Fixing Device and Image Forming Apparatus Incorporating the Same

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2024-201226, filed on Nov. 19, 2024, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

The present disclosure relates to a fixing device that heats a toner image borne on the surface of a sheet to fix the toner image onto the sheet and an image forming apparatus including the fixing device, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having at least two of copying, printing, and facsimile functions.

An image forming apparatus such as a copier or a printer in the related art includes a fixing device. The fixing device includes a pressure roller. Charge on the pressure roller is removed to prevent the occurrence of an abnormal image such as an electrostatic offset.

The present disclosure described herein provides a fixing device including a fixing rotator, a heater, a pressure roller, and a ring. The heater heats the fixing rotator. The pressure roller is pressed against the fixing rotator to form a nip through which a sheet is conveyed. The pressure roller includes a shaft extending in an axial direction and a roller body. The roller body includes a conductive surface layer having an outer circumferential surface contacting a surface of the fixing rotator at the nip. The conductive surface layer has a folded portion folded from an edge of the outer circumferential surface toward the shaft in a radial direction of the shaft. The folded portion forms at least a part of a first end face of the roller body in the axial direction. The ring is grounded and disposed on the shaft. The ring has conductivity and a second end face along the first end face in the radial direction. The second end face contacts at least a part of the folded portion.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Embodiments of the present disclosure are described below in detail with reference to the drawings. Like reference signs are assigned to like elements or components and descriptions of those elements or components may be simplified or omitted.

1 FIG. 100 With reference to, the configuration and operation of an image forming apparatusare described below.

1 FIG. 100 6 7 9 12 16 20 6 1 4 5 2 7 1 1 12 16 1 9 9 1 20 In, the image forming apparatussuch as a small printer includes a process cartridge, an exposure device, a transfer roller, a sheet feeder, a registration roller pairas a timing roller pair, and a fixing device. The process cartridgeis configured as a unit including a photoconductor drum, a charging roller, a developing device, and a cleaning device. The exposure deviceirradiates the photoconductor drumwith exposure light L that is generated based on image data input from an input device such as a personal computer. A toner image is formed on the photoconductor drum. The sheet feederincludes a feed tray to store sheets P. The registration roller pairconveys a sheet P toward a transfer nip where the photoconductor drumand the transfer rollercontact each other. The transfer rollertransfers the toner image borne on the surface of the photoconductor drumonto the sheet P conveyed to the transfer nip (that is, a transfer position). The fixing devicefixes the toner image that has not yet been fixed, to the sheet P.

4 5 2 1 1 4 5 2 6 100 6 6 100 6 The charging roller, the developing device, and the cleaning deviceare arranged around the photoconductor drum. These members (the photoconductor drum, the charging roller, the developing device, and the cleaning device) are integrated as the process cartridgeand are detachably (replaceably) attached to the body of the image forming apparatusas the apparatus body. After a user uses the process cartridgefor a predetermined replacement cycle, the user removes the process cartridgefrom the body of the image forming apparatusand replaces the process cartridgewith a new one.

1 FIG. 100 With reference to, typical processes of the image forming apparatusare described below.

7 100 7 1 The input device such as the personal computer sends the image data to the exposure devicein the image forming apparatus, and the exposure deviceirradiates the surface of the photoconductor drumwith the exposure light (a laser beam) L based on the image data.

100 1 4 1 1 4 1 1 1 1 FIG. A drive motor disposed in the body of the image forming apparatusrotates the photoconductor drumin the direction indicated by the arrow in(clockwise). Initially, the charging rolleruniformly charges the surface of the photoconductor drumat a position at which the surface of the photoconductor drumfaces the charging roller, which is referred to as a charging process. As a result, a charging potential (for example, approximately −900 V) is formed on the surface of the photoconductor drum. Subsequently, the charged surface of the photoconductor drumreaches an irradiation position of the exposure light L. An electric potential at the position that receives the exposure light L changes to a latent image potential (about 0 to −100 V), and an electrostatic latent image is formed on the surface of the photoconductor drum, which is called an exposure process.

1 5 5 1 1 After the exposure process, the surface of the photoconductor drumon which the electrostatic latent image is formed reaches the position facing the developing device. The developing devicesupplies toner onto the photoconductor drumto develop the electrostatic latent image on the photoconductor druminto a toner image, which is referred to as a developing process.

1 1 9 9 1 16 After the developing process, the surface of the photoconductor drumbearing the toner image reaches a transfer nip (that is, a transfer position) formed between the photoconductor drumand the transfer roller. In the transfer nip, a transfer bias having a polarity opposite the polarity of the toner is applied from a power source to the transfer roller, thereby transferring the toner image formed on the photoconductor drumonto the sheet P conveyed by the registration roller pair, which is referred to as a transfer process.

1 2 2 1 2 The surface of the photoconductor drumafter the transfer process reaches a position opposite the cleaning device. At the position opposite the cleaning device, a cleaning blade mechanically removes untransferred toner remaining on the surface of the photoconductor drum, and removed toner is collected in the cleaning device, which is referred to as a cleaning process.

1 Thus, a series of image forming processes on the photoconductor drumis completed.

1 9 15 12 16 16 9 1 1 The sheet P is conveyed to the transfer nip between the photoconductor drumand the transfer rolleras follows. First, a feed rollerfeeds the uppermost sheet P of the stack of sheets P stored in the sheet feedertoward a conveyance passage. Subsequently, the sheet P reaches the registration roller pair. The sheet P that has reached the registration roller pairis conveyed to the transfer nip (the contact position of the transfer rollerwith the photoconductor drum) in synchronization with an entry of the toner image formed on the photoconductor druminto the transfer nip.

9 20 20 21 31 21 21 31 21 31 100 After the sheet P passes through the transfer nip (i.e., the position of the transfer roller) in the transfer process, the sheet P reaches the fixing devicethrough the conveyance passage. In the fixing device, the sheet P is interposed between a fixing beltand a pressure roller. The toner image is fixed on the sheet P by heat applied from the fixing beltand pressure applied from both of the fixing beltand the pressure roller, which is referred to as a fixing process. After the sheet P having the fixed toner image thereon is ejected from the fixing nip formed between the fixing beltand the pressure roller, the sheet P is ejected from the body of the image forming apparatusand stacked on an output tray.

Thus, a series of the image forming processes is completed.

2 6 FIGS.to 2 FIG. 3 5 6 FIGS.,, and 20 20 20 21 24 23 30 40 31 65 With reference to, the following describes a configuration and operation of the fixing device. The fixing deviceconveys the sheet P bearing an unfixed toner image while heating the sheet P. With reference to, the fixing deviceincludes the fixing beltas a fixing rotator, a planar heateras a heat source (a heating means), a holder, a stay, a thermistor, the pressure rolleras a pressure rotator, and a gearas a ring (see).

21 31 31 21 21 21 21 24 21 21 21 2 FIG. 2 FIG. 5 FIG. a b a The fixing beltis an endless belt disposed in contact with an outer circumferential surface of the pressure rollerand driven to rotate by rotation of the pressure roller. The fixing beltis a thin, flexible endless belt driven to rotate clockwise in, that is, in a rotation direction indicated by an arrow in. With reference to, the fixing beltincludes a base layeras a belt conductive layer having an inner circumferential surface (i.e., a sliding contact surface of the fixing beltsliding over the planar heater) and a belt surface layeras a surface layer having an insulating property (or medium resistance) and being layered on the base layer. A total thickness of the fixing beltis designed to be equal to or smaller than 1 mm.

21 21 21 a a The base layerof the fixing belthas a thickness in a range of from 30 μm to 50 μm. The base layeris made of metal, such as nickel or stainless steel, or carbon-dispersed resin such as carbon-dispersed polyimide and functions as the belt conductive layer having conductivity.

21 21 21 21 21 b b b The belt surface layerof the fixing belthas a thickness in a range of from 5 μm to 50 μm. The belt surface layeris made of an insulating material such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), polyimide, polyether imide, and polyether sulfone (PES). The belt surface layerhaving the insulating property facilitates the separation of toner contained in the toner image on the sheet P from the fixing belt.

21 21 21 b b a 7 10 In the above, the belt surface layeris made of an insulating material but may be made of a material having a medium resistance by dispersing a relatively small amount of carbon in the above-described insulating material. The specific resistance value range of the medium resistance is equal to or greater than 10Ω/□ and less than 10Ω/□. As a result, the belt surface layerhas a higher resistance larger than the base layeras the belt conductive layer.

21 24 23 30 40 Inside the loop of the fixing belt, the planar heater, the holder, the stay, and the thermistorare disposed

24 31 24 21 24 31 21 24 21 21 24 24 31 21 21 31 24 2 FIG. 3 6 FIGS.to The planar heateris disposed so as to extend in a width direction that is a direction perpendicular to the surface of the paper on whichis drawn, the lateral direction in each of, and an axial direction of the pressure roller. The planar heatercontacts the inner circumferential surface of the fixing belt. The planar heateris pressed against the pressure rollervia the fixing beltto form the fixing nip through which the sheet P is conveyed. The planar heateris disposed inside the loop formed by the fixing beltsuch that the inner circumferential surface of the fixing beltslides over the planar heater. Pressing the planar heateragainst the pressure rollervia the fixing beltforms the fixing nip between the fixing beltand the pressure roller, through which the sheet P is conveyed. As described above, the planar heaterfunctions as a nip formation pad that is a member forming the fixing nip.

24 21 21 24 21 In addition, the planar heaterincludes a resistor pattern (in other words, a resistive heat generator) formed on a portion that is in sliding contact with the inner circumferential surface of the fixing belt. A power supply supplies electric power to the resistor pattern, and the resistor pattern generates heat according to the resistance of the resistor pattern to heat the fixing belt. As described above, the planar heateralso functions as a heater to heat the fixing belt.

21 24 21 21 21 24 21 21 24 24 To reduce sliding friction between the inner circumferential surface of the fixing beltand the planar heater, a lubricant such as silicon oil or fluorine grease is directly applied to the inner circumferential surface of the fixing belt. Instead of directly applying the lubricant to the inner circumferential surface of the fixing belt, the lubricant may be indirectly applied to the inner circumferential surface of the fixing beltby applying the lubricant to the sliding contact surface of the planar heateron which the fixing beltslides. In addition to applying the lubricant to the inner circumferential surface of the fixing belt, the planar heatermay include a surface layer or a sheet made of a low friction material such as PTFE on the surface of the planar heater.

23 24 23 24 24 The holderholds the planar heater. The holderhas a recess, and the planar heateris fitted into the recess to hold the planar heaterin the width direction that is the axial direction.

30 23 24 20 60 60 30 24 23 42 3 FIG. The stayholds the holderholding the planar heater. The fixing deviceincludes a frame. The frameholds both ends of the stayholding the planar heaterand the holderin the width direction via flanges(see).

24 21 21 21 24 As described above, the planar heater(the resistor pattern) disposed inside the loop of the fixing beltdirectly heats the fixing belt. The outer circumferential surface of the fixing beltheated by the planar heaterheats the toner image on the sheet P.

24 24 40 40 24 24 20 21 24 40 21 The output of the planar heateris controlled based on the temperature of the planar heaterdetected by the thermistor. The thermistordirectly contacts the planar heater(or indirectly contacts the planar heatervia another member). The fixing deviceaccording to the present embodiment does not include a temperature sensor that directly detects the surface temperature of the fixing belt. A controller controls the temperature of the planar heaterdetected by the thermistorto indirectly control the surface temperature (that is a fixing temperature) of the fixing beltto a desired temperature.

4 FIG. 42 21 21 21 42 60 60 20 42 60 42 42 42 21 21 21 21 a a With reference to, a pair of flangesguides ends of the inner circumferential surface of the fixing beltin the width direction of the fixing beltsuch that the fixing beltmaintains a substantially cylindrical posture. Specifically, the two flangesare made of a heat-resistant resin material and are held by both sides of the framein the width direction of the frameof the fixing deviceso that each of the flangescan slide and move along each of the sides of the framein a direction forming the fixing nip. Each of the flangesincludes a guideand a stopper. The guideshold the fixing beltto maintain the substantially cylindrical posture of the fixing belt. The stopper restricts motion or skew of the fixing beltin the width direction of the fixing belt.

3 FIG. 20 52 51 42 21 24 23 31 42 21 24 21 24 42 21 21 21 As illustrated in, the fixing deviceincludes pressing leversof a pressing device. The pressing levers press the flangessuch that the fixing belt, the planar heater, and the holderpress the pressure roller. The flangesare disposed to support both ends of the loop of the fixing beltin the width direction except for portions facing both ends of the fixing nip so that the planar heatercan form the fixing nip. The inner circumferential surface of the fixing beltis loosely contacted only by the planar heaterand the flangesat respective ends of the fixing beltin the width direction thereof. No other component, such as a belt guide, contacts the inner circumferential surface of the fixing beltto guide the fixing beltas it rotates.

20 30 21 31 23 24 21 30 24 23 23 24 30 60 23 The fixing deviceincludes the staythat is disposed inside the loop of the fixing beltso as to be in contact with the pressure rollervia the holder, the planar heater, and the fixing belt. The stayreinforces the planar heaterforming the fixing nip (and the holder), enhancing the mechanical strength of the holderand the planar heater. The stayis assembled to the frame(or the holder) by screw fastening or other fasteners.

30 31 23 24 21 31 24 23 30 The stayreceiving the pressure from the pressure rollervia the holder, the planar heater, and the fixing beltprevents a disadvantage that the pressure from the pressure rollerlargely deforms the planar heater(and the holder) at the fixing nip. Preferably, the stayis made of metal having an increased mechanical strength, such as stainless steel or iron, to achieve the above-described function.

23 23 23 23 31 23 The holdermay be made of resin or metal. Preferably, the holderis made of resin that has rigidity to prevent the holderfrom bending even if the holderreceives pressure from the pressure roller, and the resin preferably has heat resistance and thermal insulation. The resin may be liquid crystal polymer (LCP), polyamide imide (PAI), polyether sulfone (PES), polyphenylene sulfide (PPS), polyether nitrile (PEN), and polyether ether ketone (PEEK). The holderaccording to the present embodiment is made of liquid crystal polymer (LCP).

2 FIG. 2 FIG. 31 32 33 32 34 33 31 95 With reference to, the pressure rolleras the pressure rotator includes a cored barserving as a shaft, an elastic layerlayered on the cored bar, and a conductive surface layerlayered on the elastic layer. The pressure rolleris driven and rotated counterclockwise inby a drive motor.

32 31 33 31 The cored baras the shaft of the pressure rollerhas a hollow structure made of metal (the conductive material) and extends in the axial direction. The elastic layerof the pressure rolleris made of an insulating material such as silicone rubber foam, silicone rubber, or fluororubber.

34 31 34 34 34 33 33 34 34 6 FIG. The conductive surface layerof the pressure rolleris thin and functions as a release layer. The conductive surface layeris made of PFA or PTFE in which carbon is dispersed to have conductivity. The material of the conductive surface layerhas a tubular shape. The material of the conductive surface layeris set on the elastic layerso that the tube covers the elastic layer. Thermal processing is performed to form the conductive surface layer. The conductive surface layeris described in more detail below with reference to.

31 21 21 31 45 31 31 31 60 20 3 FIG. 2 FIG. 2 FIG. The pressure rolleris pressed against the fixing beltto form a desired nip (the fixing nip) between the fixing beltand the pressure roller. As illustrated in, a gearis attached to the pressure rollerand engages a driving gear of the drive motor so that the pressure rolleris driven and rotated counterclockwise in, that is, a direction indicated by the arrow in. Both ends of the pressure rollerin the axial direction are rotatably supported by the frameof the fixing devicethrough bearings, respectively.

20 65 The fixing deviceaccording to the present embodiment also includes the gearas the ring, which is described in detail below.

20 A description is provided of a regular fixing process to fix the toner image on the sheet P, which is performed by the fixing devicehaving the construction described above.

100 24 95 31 31 31 21 21 2 FIG. 2 FIG. When the controller in the image forming apparatusreceives a print instruction, the controller controls the power supply to supply the electric power to the planar heaterand controls the drive motorto start rotating the pressure rollerin the direction indicated by the arrow in. Due to driving and rotating the pressure roller, friction between the pressure rollerand the fixing beltat the fixing nip rotates the fixing beltin a direction indicated by an arrow in.

21 12 9 10 21 31 21 2 FIG. After the fixing beltrotates, the sheet P is fed from the sheet feeder, and the toner image is transferred onto the sheet P at the position of the transfer roller. As a result, the sheet P bears an unfixed toner image. As illustrated in, the sheet P bearing the unfixed toner image is conveyed in a direction indicated by an arrow Ywhile the sheet P is guided by the entrance guide plate and enters the fixing nip formed between the fixing beltand the pressure rollerpressed against the fixing belt.

24 21 24 23 30 31 21 24 31 11 2 FIG. The planar heaterheats the fixing belt. The planar heaterand the holderare reinforced by the stayand pressed against the pressure roller. The heat in the fixing beltand the pressure between the planar heaterand the pressure rollerfix the toner image on the surface of the sheet P. After the toner image is fixed on the surface of the sheet P, the sheet P is sent out from the fixing nip, and an exit guide plate guides the sheet P to be conveyed in a direction indicated by an arrow Yin.

20 100 The following describes the configuration and operation of the fixing devicein detail, which is characteristic of the image forming apparatusaccording to the present embodiment.

2 5 FIGS.and 21 21 21 21 21 21 21 21 21 21 21 a b a a b a b a. As described above with reference to, the fixing beltincludes the base layeras the belt conductive layer having conductivity. In addition, the fixing beltincludes the belt surface layerhaving the insulating property (or the belt surface layer having the medium resistance) directly layered on the base layer(the belt conductive layer). In other words, the fixing beltaccording to the present embodiment has a two layer structure including the base layeras the belt conductive layer having conductivity and the belt surface layerhaving the insulating property or the medium resistance and layered on the base layer. The belt surface layerhas a resistance larger than the base layer

21 21 21 21 65 21 21 21 31 65 a a b a a a 5 FIG. In particular, the fixing beltis formed so that one end of the base layer(the belt conductive layer) in the width direction that is a left end of the base layerinprojects from one end of the belt surface layerin the width direction, and the gearas the ring is disposed on the above-described one end of the base layer. In other words, the base layeras the belt conductive layer having conductivity has a portion exposed that is one end of the base layerin the axial direction of the pressure roller, and the gearas the ring is disposed on the exposed portion.

21 21 65 a b The above-described one end of the base layer(the belt conductive layer) projecting from the above-described one end of the belt surface layerin the axial direction directly contacts the gearas the ring described below (in other words, a contact portion is formed).

21 21 21 65 21 21 21 b a a b a a. 5 6 FIGS.and As a result, the belt surface layeris layered on a part of the base layer(the belt conductive layer) extending in the width direction (the lateral direction inand the axial direction) except for the contact portion on which the base layeris in contact with the geardescribed below. In other words, the belt surface layeris directly laminated on the base layerin a range extending in the width direction except for the exposed portion of the base layer

31 34 21 21 31 33 34 32 32 31 32 34 21 34 21 b On the other hand, the pressure rolleras the pressure rotator includes the conductive surface layerthat has the conductivity and is in contact with the belt surface layerof the fixing beltas the fixing rotator to form the fixing nip. The pressure rollerhas a roller body on which the elastic layerand the conductive surface layerare laminated on the cored bar. The cored baras the shaft of the pressure rollerprojects from both ends of the roller body to be exposed. The roller body does not include both ends of the cored barthat are exposed. The conductive surface layeris formed in the roller body so as to be in contact with the surface of the fixing beltat the fixing nip. In other words, the roller body includes the conductive surface layerhaving an outer circumferential surface contacting the surface of the fixing beltas the fixing rotator at the fixing nip.

5 6 FIGS.and 65 32 31 20 65 65 65 21 21 21 21 21 65 34 31 21 21 a a a b b a As illustrated in, the gearas the ring is disposed on the cored baras the shaft of the pressure rolleras the pressure rotator of the fixing device. The gearhas conductivity and is grounded. At least a part of the gearextends along an end face of the roller body. The gearas the ring contacts and is electrically connected to the exposed portion of the base layer(the belt conductive layer). The exposed portion of the base layeris an end portion of the base layerin the axial direction, and the belt surface layeris not laminated on the exposed portion. The end portion forms the exposed portion not covered by the belt surface layer. Accordingly, the gearcontacts and is electrically connected to the conductive surface layerof the pressure rollerand the base layerof the fixing belt(the belt conductive layer).

5 6 FIGS.and 65 65 65 65 65 65 65 21 21 34 31 a Specifically, as illustrated in, the gearhas a ring shape (in other words, a doughnut shape) and is made of a conductive material. However, the geardoes not have a complete ring shape. The gearhas multiple spur tooth-shaped projections on the entire outer peripheral portion of the gearin the circumferential direction. The gearis formed in a gear shape, similarly to a so-called spur gear. The gearas the ring has a shape like a gear but does not function as a gear transmitting a driving force. The gearfunctions as a conductor grounding the base layer(the belt conductive layer) of the fixing beltand the conductive surface layerof the pressure roller.

32 31 65 65 32 31 21 21 31 32 31 65 31 a 2 FIG. The cored barof the pressure rolleris inserted into the gear. In other words, the gearis disposed on the cored barof the pressure rollerso as to contact the base layer(the belt conductive layer) of the fixing beltand the end face of the roller body of the pressure roller. The cored barfunctions as the shaft of the end of the pressure roller. The gearrotates in a predetermined direction (counterclockwise in) together with the pressure roller.

65 33 34 31 65 21 21 21 a The gearhas an outer diameter (an addendum circle diameter) substantially equal to or slightly larger than the outer diameter of the roller body (that includes the elastic layerand the conductive surface layer) of the pressure roller. The tooth of the gearis in contact with the base layerof the fixing belt, which is the exposed portion of the belt conductive layer of the fixing belt.

65 31 65 21 21 21 31 21 21 31 a a b Even if the outer diameter (the addendum circle diameter) of the gearis equal to the outer diameter of the roller body of the pressure roller, the tooth of the gearcontacts the base layer(the belt conductive layer) and is electrically connected to the base layer. This is because the belt surface layeris extremely thin and the pressure rolleris pressed against the fixing beltso as to deform the fixing beltand the pressure roller.

21 21 21 21 21 a a a a The ring contacting the base layer(the belt conductive layer) of the fixing beltin the present embodiment does not have a perfect ring shape but has a gear shape (a spur gear shape in the present embodiment). The multiple gear teeth arranged at intervals in the circumferential direction intermittently contacts the base layer. The ring having the multiple gear teeth is less likely to cause a contact failure such as a partial contact than the ring having a perfect ring shape and contacting the base layer. As a result, the ring having the multiple gear teeth generates satisfactorily, stably, and relatively large contact pressure and stably electrically couples between the base layerand the ring.

65 32 32 65 32 65 32 65 32 32 60 68 65 5 FIG. The gearis press-fitted into the cored barto enhance conductivity (electrical connectivity) with the cored baras the shaft. In order to prevent the gearfrom being displaced on the cored barin the width direction (the axial direction), the gearmay be bonded and fixed to the cored barby a conductive adhesive. As illustrated in, the gearis grounded (earthed) via the cored bar. Specifically, the cored baris connected to a grounding wire including the framegrounded via a resistor(an electric resistance member). Thus, the gearis favorably grounded.

65 20 65 The gearis disposed outside a maximum sheet passing region M in the fixing device(in other words, disposed in a non-sheet passing region). The maximum sheet passing region M is defined as a region in the width direction through which a sheet P having a maximum size that can be conveyed passes. As a result, the geardoes not contact the fixed image and does not affect the fixed image.

20 65 65 21 21 34 31 21 31 a As described above, the fixing deviceaccording to the present embodiment includes the gearfunctioning as the conductor. The gearis grounded and satisfactorily and electrically connected to the base layer(the belt conductive layer) of the fixing beltand the conductive surface layerof the pressure roller. The above-described structure is less likely to accumulate electric charge in the fixing beltand the pressure rollerand reduces the occurrence of an abnormal image such as an electrostatic offset caused by the electric charge accumulation.

21 21 21 The electrostatic offset occurs as follows in the fixing process. When the sheet P that bears the toner enters the fixing nip, the toner electrostatically moves and adheres to the fixing beltas the fixing rotator. After the fixing beltrotates once, the toner adhered to the fixing beltadheres to the sheet P again. As a result, the electrostatic offset occurs.

21 21 31 21 21 31 31 21 The above-described movement of toner to the fixing beltis caused by charge on the surfaces of the fixing beltand the pressure roller. In the present embodiment, the toner is negatively charged. when the fixing beltis positively charged, the toner receives an electrostatic adsorptive force from the fixing belt. When the pressure rolleris negatively charged, the toner receives an electrostatic repulsive force from the pressure roller. As a result, the toner adheres to the fixing belt.

20 21 21 34 31 21 31 a To countermeasure the above-described phenomenon, in the fixing deviceaccording to the present embodiment, the charge is removed from the base layer(the belt conductive layer) of the fixing beltand the conductive surface layerof the pressure rolleras described above. As a result, the surfaces of the fixing beltand the pressure rollerare less likely to be charged. Therefore, electrostatic offset is less likely to occur.

6 FIG. 5 6 FIGS.and 34 31 34 31 65 34 a a. As illustrated in, the conductive surface layerof the pressure rolleraccording to the present embodiment has a folded portionforming one end of the roller body in the axial direction that is the left end of the pressure rollerin. The gearas the ring is disposed adjacent to the folded portion

34 31 31 31 34 34 33 34 34 34 34 34 33 33 a a a The material of the conductive surface layerof the pressure rolleris folded from an edge of the outer circumferential surface of the pressure rollertoward the center axis W of the pressure rollerto form the folded portion. The folded portionforms the whole of the end face of the roller body including the elastic layerand the conductive surface layerbut may form a part of the end face of the roller body. The folded portionhas a shape in which the conductive surface layeris folded but may not made by a manufacturing process that actually folds the material of the conductive surface layer. In particular, the conductive surface layerin the present embodiment has a tubular shape substantially covering the entire outer peripheral surface of the elastic layerand the end faces of the elastic layer.

34 65 34 33 34 65 34 34 34 65 32 65 65 34 a a a a. 5 6 FIGS.and The almost entire of the folded portioncontacts the end face of the gearas the ring. In other words, one end of the conductive surface layerin the width direction (in other words, one end in the axial direction) has a shape folded in the radial direction and extending along the end face of the elastic layeras illustrated in. The portion of the conductive surface layerhaving the shape folded in the radial direction contacts the end face of the gear. As a result, the conductive surface layerhas the folded portionfolded from the edge of the outer circumferential surface toward the shaft in the radial direction of the shaft, and the folded portionforms at least a part of the end face as a first end face of the roller body in the axial direction. In addition, the gearas the ring is grounded and disposed on one end of the cored baras the shaft in the axial direction. The gearhas conductivity. The gearas the ring has a second end face along the first end face of the roller body in the radial direction, and the second end face of the gear contacts at least a part of the folded portion

34 34 65 34 65 a Bringing the folded portionformed in the conductive surface layerinto contact with the end face of the gearas described above, which is a relatively simple configuration, can obtain a sufficient contact area between the conductive surface layerand the gearwithout providing a complicated ground path.

34 31 As a result, the charge in the surface (the conductive surface layer) of the pressure rolleris sufficiently removed, and the occurrence of the abnormal image such as the electrostatic offset is sufficiently reduced.

The following describes a first modification.

7 FIG. 20 65 31 65 As illustrated in, the fixing deviceaccording to the first modification includes the gearthat has an edge facing the roller body of the pressure roller. At a room temperature, the edge of the gearas the ring is separated from an edge of the outer circumferential surface of the roller body to form a gap. The room temperature is typically from 15° C. to 28° C.

65 2 1 1 2 65 34 31 34 34 31 1 65 65 a a Specifically, the gearin the first modification has a substantially drum shape in which a gear width Dof an outer diameter portion is smaller than a gear width Dof an inner diameter portion (D>D). In other words, the gearas the ring includes a drum. The conductive surface layerof the pressure rollerhas a folded portionformed as one end of the roller body in the axial direction. A part of the folded portionadjacent to the shaft of the pressure rolleris in contact with the inner diameter portion having the gear width Dof the gearand is electrically connected to the gear.

65 20 65 65 The reason why the gearhas the above-described shape is as follows. In the fixing process (an actual use state), the fixing deviceis used at a high temperature. The thermal expansion of the outer diameter portion of the gearis likely to be larger than the thermal expansion of the inner diameter portion of the gear.

7 FIG. 65 20 32 65 In particular, as illustrated in, the gearas the ring in the fixing deviceaccording to the first modification has the inner circumferential surface as the bonding portion R bonded to the cored baras the shaft via a conductive adhesive. The adhesive on the bonding portion R restricts the thermal expansion of the inner diameter portion of the gear. As a result, the thermal expansion of the outer diameter portion is larger than the thermal expansion of the inner diameter portion, and the gear width at the high temperatures becomes larger than that at the room temperature.

8 FIG. 8 FIG. 65 65 65 31 33 34 34 33 31 34 is a sectional view of the gearaccording to a comparative example. At the room temperature, the gearaccording to the comparative example has a constant gear width from the inner diameter portion to the outer diameter portion. However, at the high temperature during the fixing process, the gear width of the outer diameter portion becomes larger than that of the inner diameter portion due to the thermal expansion. In such a case, the gearhaving the gear width of the outer diameter portion increased by the thermal expansion presses the end face of the roller body of the pressure roller, which causes wrinkles at the end of the elastic layeror a raised portion in an end of the conductive surface layer(see a part F surrounded by a broken line in). Such phenomena damage the conductive surface layerand the elastic layer, reduce the function as the pressure rollerforming the fixing nip N, and cause difficulty in grounding the conductive surface layer.

65 20 2 20 65 8 FIG. In contrast, the gearin the fixing deviceaccording to the first modification is designed to have the gear width Dof the outer diameter portion set to be small in advance at the room temperature in anticipation of the gear width being increased due to the thermal expansion at the high temperature during the fixing process as described above. In other words, the fixing deviceaccording to the first modification is designed to have a clearance for the thermal expansion of the outer diameter portion of the gear. As a result, the disadvantages described with reference toare less likely to occur.

34 65 34 65 31 34 65 34 65 a 7 FIG. Also in the first modification, the part of the folded portionin contact with the end face of the geargives a sufficient contact area between the conductive surface layerand the gear, and thus the charge on the surface of the pressure roller(in other words, the conductive surface layer) can be satisfactorily removed. In particular, the thermal expansion of the outer diameter portion of the gearat the high temperature during the fixing process further causes the contact area between the conductive surface layerand the gearto be larger than the contact area under the room temperature illustrated in, and thus the above-described charge removing effect is more likely to be exhibited.

The following describes a second modification.

9 FIG.A 7 FIG. 9 FIG.A 7 FIG. 9 FIG.A 20 65 31 31 65 65 65 65 As illustrated in, the fixing deviceaccording to the second modification includes the gearthat is disposed on the pressure rollerand has the edge facing the roller body of the pressure roller. At the room temperature, the edge of the gearas the ring is separated from the edge of the outer circumferential surface of the roller body to form the gap, which is the same as the embodiment illustrated in. However, the shape of the gearillustrated inis different from the drum shape illustrated in. The gearhas one end face facing the roller body and having a shape like the drum shape and the other end face (the left end face of the gearin) being flat and having a straight line in the cross section.

65 65 31 65 31 21 21 65 65 65 65 34 34 x x a x x x a 9 FIG.B The gearas the ring in another example of the second modification includes a small-diameter portionfacing the roller body of the pressure rolleras illustrated in. The small-diameter portionis sufficiently smaller than the outer diameter of the pressure rollerand does not contact the base layerof the fixing belt. In other words, the gearas the ring includes the small-diameter portionas a portion facing the roller body, and the small-diameter portionas the portion has a diameter smaller than a diameter of the roller body. An end face of the small-diameter portionis in contact with the folded portionof the conductive surface layer.

65 65 65 65 31 65 31 21 21 9 FIG.C 9 FIG.C z a As still another example, the gearas the ring has a groove at a position in the axial direction in the outer circumferential surface of the gearas illustrated inat the room temperature. The groove extends in a circumferential direction of the gearas the ring. Specifically, the gearhas the groove in a medium part of the gear in the axial direction that is a width direction of the gear. In the example of, the groove is relatively close to the end face of the roller body of the pressure roller. A bottom portionof the groove is sufficiently smaller than the outer diameter of the pressure rollerand does not contact the base layerof the fixing belt.

65 65 65 31 33 34 9 9 FIGS.A toC Since the gearillustrated in each ofhas the clearance for the thermal expansion of the outer diameter portion of the gear, the disadvantages caused by the outer diameter portion of the gearpressing the end face of the roller body of the pressure rolleris less likely to occur. As a result, the disadvantage of wrinkles occurring at the end of the elastic layerand the disadvantage of the end of the conductive surface layerrising are less likely to occur.

20 34 65 34 65 31 34 9 9 FIGS.A toC a Also in the fixing deviceas illustrated in each of, a part of or the entire of the folded portionin contact with the end face of the geargives a sufficient contact area between the conductive surface layerand the gear, and thus the electric charge on the surface of the pressure roller(in other words, the conductive surface layer) can be satisfactorily removed.

The following describes a third modification.

10 FIG.A 34 31 20 34 a As illustrated in, the conductive surface layerof the pressure rollerin the fixing deviceaccording to the third modification has multiple folded portionsseparated in the circumferential direction so as not to overlap each other.

34 34 33 a The multiple folded portionsmay be formed when the material of the conductive surface layeris spread on and attached to the elastic layer.

34 34 34 65 10 FIG.A a a specifically, the conductive surface layerillustrated inhas two folded portionsdisplaced from each other by 180° not to overlap each other. The above-described configuration provides stable and good contact (conduction) between the multiple folded portionsand the end face of the gear.

10 FIG.B 10 FIG.B 34 65 34 a a A comparative example is described with reference to. As illustrated in, overlapping multiple folded portionsgenerates a step between an overlapping portion and a non-overlapping portion, and the step is likely to prevent the gearand the folded portionsfrom providing the stable and good contact (conduction).

34 65 65 65 65 34 a k k a. 10 FIG.A The folded portionillustrated inhas a portion contacting an end face contact portionof the gear, and the portion is larger than another portion to increase the contact area between the end face contact portionof the gearand the folded portion

20 34 65 34 65 31 34 a Also in the fixing deviceaccording to the third modification, the folded portionin contact with the end face of the geargives a sufficient contact area between the conductive surface layerand the gear, and thus the charge on the surface of the pressure roller(in other words, the conductive surface layer) can be satisfactorily removed.

The following describes a fourth modification.

11 FIG. 11 FIG. 31 20 34 34 34 1 34 1 31 31 a a a As illustrated in, the pressure rollerin the fixing deviceaccording to the fourth modification has a gap between the end face of the roller body and the folded portionof the conductive surface layerin a partsurrounded by a broken line in. The partis close to the surface of the pressure roller(the outer circumferential surface of the pressure roller).

34 31 34 34 31 34 1 34 1 31 34 1 65 65 a a a a a a x In other words, the folded portionin the fourth modification has a portion that is close to the outer circumferential surface of the roller body of the pressure rollerand not bonded to the end face of the roller body. The folded portionhas the portion separated from the end face of the roller body at a position close to the edge of the outer circumferential surface of the roller body in the axial direction. The folded portionis bonded to the end face of the pressure rollerin a part other than the partsurrounded by the broken line (the partforming the gap between the end face of the pressure roller). The part of the folded portion other than the partcontacts and is electrically connected to the small-diameter portionof the gear.

34 31 31 34 34 31 32 65 32 65 31 32 a a x The material of the conductive surface layeris folded from the edge of the outer circumferential surface of the pressure rollertoward the center axis W of the pressure rollerto form the folded portionin the fourth modification, and the folded portionin the fourth modification forms a part of the end face of the roller body of the pressure roller(the part close to the cored bar). A part of the gear(the part close to the cored bar, the small-diameter portion) extends along the end face of the roller body of the pressure rollerand is disposed on the cored bar.

34 31 34 21 34 21 a a Vertically folding the material of the conductive surface layerfrom the edge of the outer circumferential surface of the pressure rollerto form the folded portionmay generate a protrusion (in other words, a bulge), and the protrusion is likely to damage the fixing belt. Not bonding the part of the folded portionclose to the outer circumferential surface of the roller body to the end face of the roller body and forming the gap can prevent the fixing beltfrom being damaged.

20 34 65 34 65 31 34 a Also in the fixing deviceaccording to the fourth modification, the folded portionin contact with the end face of the geargives a sufficient contact area between the conductive surface layerand the gear, and thus the charge on the surface of the pressure roller(in other words, the conductive surface layer) can be satisfactorily removed.

20 24 21 31 24 21 31 21 31 34 34 31 21 65 65 32 31 34 34 31 31 34 65 31 34 65 a a a As described above, the fixing deviceincludes the planar heateras the heater, the fixing beltas the fixing rotator, and the pressure rolleras the pressure rotator. The planar heaterheats the fixing belt. The pressure rolleris pressed against the fixing beltto form the fixing nip N through which the sheet P is conveyed. The pressure rollerincludes the conductive surface layerhaving conductivity. The conductive surface layeris formed on the roller body of the pressure rollerto contact the surface of the fixing beltat the fixing nip N. The gearas the ring has conductivity and is grounded. The gearis disposed on the cored bar(as the shaft) of the pressure rollersuch that at least a part of the gear contacts along the end face of the roller body. The conductive surface layerhas the folded portionhaving the shape folded from the edge of the outer circumferential surface of the pressure rollerto the center axis of the pressure roller. The folded portionforms a part or the whole of the end face of the roller body. The gearis disposed on the end of the roller body in the axial direction of the pressure rollerthat is the same as the width direction. The part or the whole of the folded portionis in contact with the end face of the gear.

31 The above-described configuration can sufficiently remove the charge on the surface of the pressure roller.

20 24 In the above embodiments and modifications, the present disclosure is applied to the fixing deviceincluding the planar heateras the heater. However, the fixing device to which the present disclosure is applied is not limited to this. For example, the present disclosure may be applied to the fixing device including an electromagnetic induction coil as the heater.

20 21 In the above embodiments and the modifications, the present disclosure is applied to the fixing deviceincluding the fixing beltas the fixing rotator. However, the fixing device to which the present disclosure is applied is not limited to this. For example, the present disclosure may be applied to the fixing device including a fixing roller or a fixing belt stretched around multiple rollers as the fixing rotator.

21 21 21 21 21 21 21 21 21 a b a b a b a In the above embodiments and modifications, the fixing beltincludes the base layeras the belt conductive layer. Alternatively, the fixing beltmay include the belt surface layerand a conductive elastic layer sequentially layered on the base layerto form a three layer structure. In this case, the belt surface layeris indirectly layered over the base layer. The belt surface layerdirectly or indirectly layered over the base layermay be expressed as the belt surface layer over the base layer. The conductive elastic layer may be used as the belt conductive layer.

65 In the above embodiments and modifications, the fixing device includes the gearas the ring. However, the ring does not necessarily have to be the gear. In addition, the ring does not necessarily have to be the spur gear. For example, the ring may be the helical gear.

24 31 21 In the above embodiments and modifications, the planar heateras the heater serves as the nip formation pad and is pressed against the pressure rollervia the fixing beltto form the fixing nip. However, the nip formation pad may not be the heater.

65 34 31 21 21 65 34 31 21 21 a a a a In the above embodiments and modifications, the gearas the ring contacts the folded portionof the pressure rollerand the base layerof the fixing beltto form the grounding path. However, the gearas the ring may contact the folded portionof the pressure rollerto form the grounding path, and the base layerof the fixing beltmay form another grounding path.

The above-described configurations also provide similar effects to those of the above-described embodiments and the modifications.

Note that embodiments of the present disclosure are not limited to the above-described embodiments, and it is apparent that the above-described embodiments can be appropriately modified within the scope of the technical idea of the present disclosure in addition to what is suggested in the above-described embodiments. Further, features of components of the embodiments, such as the number, the position, and the shape are not limited the embodiments and thus may be preferably set.

In the present description, the term “sheet” is defined as any sheet-like recording medium including all conveyed objects, such as typical paper, coated paper, label paper, overhead projector (OHP) transparency, or a film sheet.

Aspects of the present disclosure may be, for example, as follows.

In a first aspect, a fixing device includes a fixing rotator, a heater heating the fixing rotator, a pressure roller pressed against the fixing rotator to form a nip through which a sheet is conveyed, and a ring. The pressure roller includes a roller body with a conductive surface layer. The conductive surface layer has conductivity and contacts the surface of the fixing rotator at the nip. The ring has conductivity and is grounded. The ring is disposed on the shaft of the pressure roller such that at least a part of the ring extends along an end face of the roller body. The conductive surface layer has a folded portion folded from an edge of an outer circumferential surface of the roller body to the center axis of the roller body such that the folded portion forms a part or the whole of the end face of the roller body. The folded portion is in one end portion of the roller body in a width direction, the one end facing the ring. The part or the whole of the folded portion is in contact with the end face of the ring.

In a second aspect, the fixing device according to the first aspect includes a fixing belt as the fixing rotator. The fixing belt consists of a belt conductive layer with conductivity and a belt surface layer with insulating properties or medium resistance. The belt surface layer is directly or indirectly layered on part of the belt conductive layer, except for an exposed portion at the end of the belt conductive layer in the width direction. The end of the belt conductive layer is closer to the ring than the other end in the width direction. The ring contacts and is electrically connected to the exposed portion of the belt conductive layer.

In a third aspect, the ring in the fixing device according to the second aspect has a gear shape, and a tooth of the gear shape is in contact with the exposed portion of the belt conductive layer.

In a fourth aspect, the ring in the fixing device according to any one of the first to third aspects has an edge facing the roller body and is configured to form a gap between the edge of the ring and the edge of the outer circumferential surface of the roller body at a room temperature.

In a fifth aspect, the ring in the fixing device according to the fourth aspect has a substantially drum shape.

In a sixth aspect, the ring in the fixing device according to the fourth aspect includes a small-diameter portion facing the roller body.

In a seventh aspect, the ring in the fixing device according to any one of the first to the third aspects has a groove formed in a part of an outer circumferential surface in a width direction at a room temperature.

In an eighth aspect, the ring in the fixing device according to any one of the first to seventh aspects has an inner circumferential surface bonded to the shaft.

In a ninth aspect, the fixing device according to any one of the first to eighth aspects includes another folded portion that is separated from the folded portion in a circumferential direction of the end face of the roller body and does not overlap the folded portion.

In a tenth aspect, the folded portion in the fixing device according to any one of the first to ninth aspects is configured to form a gap between the end face of the roller body and a part of the folded portion close to the edge of the outer circumferential surface of the roller body.

In an eleventh aspect, an image forming apparatus includes the fixing device according to any one of the first to tenth aspects.

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.